Reference may be made to the following U.S. Pat. Nos. of interest: 3,383,487; 3,860,771; 3,862,381; 3,862,382; 4,017,848; 4,056,699; and 4,066,851.
Currently, the most commonly used types of touch actuated panel switch devices comprise either the glass-capacitive or the flexible plastic membrane type switches. The glass-capacitive touch panel switches are presently employed in elevators for selecting floors, in microwave ovens for selecting various oven control or display functions, etc. They offer the advantage of being readily imprinted with desired graphic information, thereby presenting a smooth, aesthetic panel effect, while also having a desirable tactile effect in operation. On the other hand, the glass panels are relatively expensive to construct, difficult to interface with electronic control circuits and subject to relatively easy breakage. In addition, the "touch" operating reliability of the capacitive type switches employed is subject to humidity, temperature, human physiology factors, and other conditions so that at times several attempts at switch actuation must be made before the switch operates.
Touch actuated membrane type switches employ printed circuit contactors on a flexible, thin plastic surface aligned over printed switch contacts positioned on an opposite non-conductive surface, with an insulating spacer between having holes in registration with each switch contact position. The flexible plastic surface is deflected over a spacer hole to move the switch contactor between about 10-25 mils to engage the contactor with its associated contact. Such membrane type switches while less expensive to construct and generally more reliable in switching operation than the glass-capacitive touch switches, present several problems of their own when utilized in touch actuated panels.
In particular, the plastic front panel, usually formed of a thin, flexible polyester sheet, cannot be graphically imprinted as well nor is it as pleasing in its aesthetic appearance compared to the smooth glass panels. Also, the rather spongy feeling during "touch" operation is an undesirable tactile aspect when compared to a "touch" operated smooth glass panel. In addition, the flexible front panel plastic sheet is readily subject to damage from sharp objects and to undesirably enabling contact with a small but possibly deadly voltage on the printed circuit conductors. Some membrane switches incorporate a vent or air channel to couple the air space in each spacer hole to the atmosphere so as to allow deformation of the flexible front panel without requiring an undesirably excessive amount of deflecting pressure to be exerted or in an attempt to eliminate the spongy switch operation. Yet, many applications require these switches to be placed in a generally hostile environment--high temperatures, high moisture conditions, or a greasy, dirty or dusty situation, and thus, such hostile environment could adversely affect the switch operating reliability.
A significant further disadvantage is the requirement to registerably align each of the spacer holes with a respective switch contact position during assembly and to provide means for maintaining this precise alignment. While each spacer hole could be made larger to more readily enable alignment with the respective switch contacts, too large of a hole would permit the flexible sheet to depress over too large of an area and thereby undesirably operate two or more switches rather than only the one switch desired. On the other hand, in order to reduce the possibility of undesirably operating two switches when only one is desired, the spacer hole should be made as small as possible. However, reducing the spacer holes leads to increasing the problem of aligning a respective hole with its contacts.
It is therefore desired to provide a touch panel switch device combining the respective advantages of glass type capacitive switches and of the depressable plastic type membrane switches without the disadvantages of either.